The desirability of fabricating metal into useful implements and objects have long been known and available fabrication techniques are varied. In the particular area of fabricated tubular members, it is often useful to further fabricate an end portion thereof to form a neck so the tube opening has a diameter that is smaller in size than the diameter of the original tube and, therefore, of the remaining tube body. A particular industry which widely employs a necking procedure and the industry to which the present invention is specifically directed is the container industry wherein tubular members are fabricated into containers adapted to receive goods for packaging. Such containers may be beverage containers, spray cans, food packaging containers, and the like.
In some instances, containers as described above are made from a metal tubular body which is enclosed at opposite ends by a bottom end structure and a lid structure. This type of three-piece construction is commonly employed, for example, in many types of aerosol containers. In such constructions it is relatively easy to provide forming dies or punches which can conveniently neck one end of the tubular body since the interior die or punch can easily be removed from the open end remaining after the opposite end has been reduced in size to form the neck. One such example is shown in U.S. Pat. No. 4,173,883 issued Nov. 13, 1979 to Boik. In this patent, it is taught how a cylindrical body blank may have one end portion progressively reduced in diameter to form a neck in the shape of a frustoconical dome by means of a plurality of inside tools in the form of punches and a plurality of outside tools in the form of dies which configure the end portion of the neck in a stepwise manner.
A different problem, however, occurs when it is desired to neck the open end of a two-piece can of the common type of metal containers used in the beer and beverage industry. These cans, whether made of aluminum or tin plated steel, have a cylindrical body formed with an integral bottom end wall. A separately formed top end or lid portion is double seamed onto the open end of the can body after the can has been filled with product. The desirability for necking the open end of the cylindrical can body prior to filling the can with product and seaming on the lid is well known. On one hand, the reduction in diameter adjacent its top is sufficient to provide space within the geometric projection of the outer diameter of the can body for the rim or chime formed on the outer side of the top edge of the lid when the lid is applied to the can body. When necking is omitted, the chime protrudes radially outwardly beyond the geometric projection of the container body and interferes with the efficient packing of the containers where a manufacturer desires to have the container bodies in close contact with one another without the spacing caused by the protruding rims. Furthermore, it is desirable to recess the rims within the cylindrical projection of the can body in order to be compatible with certain dispensing equipment.
On the other hand, and perhaps of greater importance, it is desirable to reduce the opening size of the container in order to reduce the diameter of the lid which is to be seamed thereon. Where such containers are aluminum cans, as is now the standard practice used in the soft drink or beer industry, the lid panel must be made of a metal thickness gauge that is on the order of at least twice the thickness of the can sidewall. By minimizing the opening size, the amount of total metal used in construction is reduced without sacrificing the structural integrity of the container sidewall. This can result in substantial cost savings for the can manufacturer and user as well as being more efficient from the standpoints of energy and materials usage.
Can manufacturers and fillers have heretofore been known to utilize two types of necking systems to reduce the diameter of the open end of a tubular can. One such technique is known as "spin-necking" and the other is known as "die-necking." Where progressive die sets are used in die-necking, the open end is sequentially formed by a plurality of die sets to produce an inwardly tapering neck portion. However, die-necking often produces noticeable circumferential steps or rib lines along the neck which correspond to each of the die sets used in the progressive fabrication. It is known to sometimes reform the neck end portion with an external forming roller to eliminate at least some of the steps or ribs to produce a frustoconical portion having a substantially more uniformed inwardly curving neck wall. In the spin-necking procedure, a plurality of die necking operations reduce the diameter of the container neck. Forming rollers rotate about the circumference of the necked container as it is withdrawn from the forming station in order to smooth out circumferential ridges formed when the neck was initially formed. Despite the use of those forming rollers, undesirable circumferential rib lines often remain on the neck surface. Furthermore, it has been found that spin-necking stretches and thins the neck metal which thereby weakens the neck and, it is even possible that the necked end portion of the can will have a distortion in symmetry which can create problems in seaming a lid thereon.
Accordingly, while there have been substantial developments in metal fabrication techniques for necking the open end of a tubular member and specifically the open end of a tubular can having a closed end formed integrally with the cylindrical sidewall thereof, there remains a need for improved structures which can form necked portions for such tubular members and cans so that the necks have a smooth pleasing appearance, uniformity, structural integrity, etc. There is further a need for apparatus and methods for necking tubular members and cans which can operate at high speeds with reduced risk of breakdown due to simplified construction. There is a further need for improved manufacturing equipment and methods employed thereby which equipment is relatively durable and which requires low maintenance.